During athletic endurance and weight training the intention is to stress portions of the skeletal muscles as large as possible over extended periods of time. This is the case, for example, during cross-country skiing or during swimming, i.e. in the course of types of athletics which have been particularly lauded time and again for their beneficial effects on the body.
During running and walking, which are the natural means of human propulsion, the legs alone are almost exclusively used and the arms perform involuntary load-free motions during running or walking.
In order to put more of a load on the limbs, weights are strapped to the wrist and ankles; however, these weights offer more of a resistance to the corresponding flexor muscles. However, during running and walking the more important muscles are the extensor muscles which support the body and trigger a jump.